On Wed, 30 Jan 2008 10:36:37 GMT, Ryan Cousineau <[email hidden]>
Quoted message said:I think that while this exception is interesting, Carl's broad assertion
("about the only vehicle..."😉 holds up, and that his explanation is
reasonable. I don't think the handcar offers a way forward for HPV
drivetrains.
Dear Ryan,
Actually, it was Andrew Muzi who said that in this thread, not me.
Jobst has pointed it out, too, as he mentions in this thread.
I agree with them. Most vehicles are powered by engines, few of which
work as slowly as legs and arms, so they gear down.
Engines aren't included in bicycles or railroad handcars, so they gear
up to suit their powerplants.
Trials riding offers a good example. The crank of a bicycle bumping
over obstacles is turning at RPM that you can count on your fingers,
while the motorcycle engine is idling at RPM higher than a bicycle
sprinter.
Same thing with boats. The long arm of an oar is gearing up in the
sense that it trades force for distance--the paddle moves further
through the water than the hand holding the other end. Boat
propellers, on the other hand, are geared down to turn at lower RPM
than the engines frantically powering them.
Even airplane engines can be considered as gearing down. Prop RPM is
usually slower than engine RPM, with the engine speed typically being
held constant while the variable-pitch blade functions as the
equivalent of a CVT.
The Gossamer Condor is a curious exception. The rider pedaled at 110
RPM for takeoff and 98 RPM for level flight, with the prop turning at
about 120 RPM. But the butterfly-slow aircraft was really just a
slow-motion 10-foot elevator. Almost all the rider's effort was going
into maintaining the pressure difference between the top and bottom of
the huge wing to keep his own weight plus the aircraft up off the
ground.
In other words, a rider in a human-powered aircraft can't use normal
high bicycle gearing to trade force for distance. He's really pedaling
his guts out to raise himself a few feet up, not forward.
Cheers,
Carl Fogel
